For two decades, Tycho and his assistants at Uraniborg produced thousands of astronomical observations of unprecedented quality. Tycho’s large-scale observing instruments, together with sophisticated new error correction techniques, increased observational precision by a factor of twenty. His star positions were accurate to within 1 minute, or 1/60th of a degree. The absence of stellar parallax, predicted by Copernicus, became even more puzzling given the increased precision achieved in Tycho’s monumental observing program.